As a method for inspecting a foreign substance or a residue (hereinafter simply referred to as a “foreign substance”) adhering to the inside of the container, Patent Document 1 discloses a method in which a foreign substance or any other substance adhering to the inside of the drum is inspected using an image of the inside of the drum. In this method, an illuminating lamp and a camera are inserted into the drum, and while the inside of the drum is illuminated with the illuminating lamp, the image is captured by the camera.